In the aerospace industry, over recent times carbon fibre reinforced composites (for example composites containing carbon fibres and epoxy resin) have become an increasingly attractive alternative to metal for many aircraft components. The carbon fibre reinforced composite material offers improved properties such as lower weight, improved fatigue/damage resistance, corrosion resistance and negligible thermal expansion.
In aerospace applications ducts (for example an aero-engine duct or nacelle) that include a flange to facilitate connecting sections of the duct to each other and to mount engine components to the duct are commonly made from metal. An example of a conventional flange is a disc shaped rim formed on the end of pipes and shafts for coupling them together. Conventionally, flanges are included on, for example, metallic hollow structures such as pipes for joining two such structures together or for joining a hollow structure to surrounding structural elements, for example a flange on an aero-engine duct or nacelle facilitates attaching sections of the duct to each other and for mounting engine components to the engine housing.
To produce a flange that forms a disc shaped rim on a hollow structure from composite materials involves complex manufacturing processes due to the importance of maintaining uniformity of fibre alignment and the importance of keeping any discontinuities due to creasing etc or voids in the composite structure to a minimum, in particular, in a flange that is to be used in a load bearing application because any such faults would likely produce a product having inferior properties to those that the component was designed for.
Due to the complexities in manufacturing a duct with an integral flange from composite material, such components for use in aerospace applications (for example as an aero-engine duct or nacelle) are commonly made from metal. FIGS. 10A and 10B illustrate an outer engine duct and an inner engine duct respectively showing examples of sections of the duct that are joined together at adjacent flanges indicated by reference A1.